Stabilized acrylonitrile polymers



Patented Dec. 1, 1953 UNITED STATES? PATENT? OFF lClEa Robert J. Slocombe; Dayton, and George L. Weep,

Englewod,"0hio,' assignors to'Monsanto Chem ical Company, St-. Louis, Mo'l,'a corporation-t of Delaware No'Drawing. Application October 26; 195.0,

Serial No. 192,342

Claims; (Cl. 260-4532) This invention relates to inethods of prepar-- ing polymers of acrylonitrile which are stabilized with respect to'thermodisooloration. More-'specificallythe invention relates to methods of converting unstable polymers of acrylonitrile into color stable polymers.

Although polyacrylonitrile and copolymersof 50*per cent or moreby weightof acrylonitrile and other monomers containing olefinic unsaturation copolymerized "therewith; are generally regarded as being materialsof good thermostability; they are subject ac-discoloration. This phenomenon generally results because of the need for extruding and molding the composition at elevated temperatures. Furthermore the higher :acryloriitrile polymers find extensive use in the fabrication of fibers, films and fabrics which frequently are subjected to ironing operations at elevated temperatures. Thus, serious discolora tions areoften developed in the fabrication and processing of acrylonitrilepolymers.

The primary purpose of this invention is to provide color stable polymers of .acrylonitrile." A.

further purpose of the invention is to i facilitate in-Ithe polymer It may-be that'the aluminum ions react with the impurity to form a substance which is more heat stable than the impurity in its original form. Since not all aluminum compounds produce the same beneficial effect the phenomena apparently involve additional stabilization by the anion as well as the cation. The total stabilization may involve additive or synergistic effects. Irrespective of the mechanism, it has been found that a very wide variety of aluminum salts produces the desired effect.

The acrylonitrile polymers with which this invention may be practiced include polyacrylonitrile and copolymers of from 20 or more per cent acrylonitrile and up to 80 per cent of one or more of a wide variety of other unsaturated substances known to be copolymerizable with the acrylonitrile. Thus, the invention is practicable'with' the well-known fiber forming copolymers of acrylonitrile, which may be the co= polymers of lfiper cent or moreper cent-of acrylonitrile andup to 25 per cent of othermonomers. Other copolymers of from-'25' 'per cent toper cent acrylonitrile and '75 to -25 percent of the various othermonomers, which copolymers have primary utility in th'e' fieldof film andmolding composition production,-are also useful.

The said other monomers with-"which the acry lonitrile may be copoly'merized to produce resinous substances capable of use in the practice of this invention include-vinyl acetate and other vinyl esters of monocarboxylic acids having up to fourcarbon atoms in-the carboxylic acidmar: cal, dimethyl maleate and dimethyl fumarate and other alkyl esters of fumaric and maleicacidsg wherein the alkyl radical hasup to four carbon 5 atoms, methyl methacrylateor acrylate and 'oth'er alkyl acrylates'and alkyl methacrylateswherein the alkyl radical has up to four carbon atomsp vinyl chloride and other vinyl halides,--styrene,

a-methylstyreneand other vinyl and isopropen-ylj substituted aromatichydrocarbons, methacr-ylo nitrile, vinylidene chloride, vinylpyr-idine th'e" vinyl derivatives of other alkyl substituted pyridines, and the vinyl derivatives of other componnds containing a tertiary amino atom; in -a heterocyclic ring,. vinylchloroa cetateand other: vin'yl esters of haloaeetic'acids, methallyl, chloro acetate, allyl chloroacetate and chloroallylch1oro-,. acetate-and thecorrespondingesters of others; haloaceticj esters, 'vinylimidazole and other 'N- vinyl-derivatives of; heterocyclic nitrogen compounds, and one or more of these and other nne saturated z-compounds known to be copolymer-- izable with acrylonitrile.

The aluminum salts which are useful in the practice of this invention include for example aluminum chloride, aluminum sulfate, aluminum nitrate and aluminum borate. In the practice of this invention the aluminum salt may be used to the extent of 0.01 per cent to ten per cent by weight of the acrylonitrile polymer to be stabilized. Preferred practice of this invention involves the use of 0.1 per cent to three per cent of the stabilizer.

The invention may be practiced by combining the acrylonitrile polymer and the aluminum salt by a wide variety of mechanical procedures. Thus, the polymer may be treated in granular solid form and mixed physically with the solid aluminum salt or an aqueous or other liquid solution or dispersion of the aluminum salt- The physical mixture may take place at room temperature or at higher temperatures, for example the temperature at which the polymer is semisolid or fluid. A preferred practice involves the use of solvents or plasticizers for the acrylonitrile polymers in the presence of which the intimate dispersing of the stabilizing additive and the acrylonitrile polymer is more readily effected. The nature of the solvent which is useful in dissolving or softening the acrylonitrile polymer will to a large extent depend upon the chemical composition of the acrylonitrile polymers.

The copolymers of 75 per cent or more of acrylonitrile and up to 25 per cent of the comonomer are well-known fiber forming compositions and are generally resistant to the eiiect of most chemical solvents. In the preparation of solutions of such copolymers, solvents, such as N,N dimethylformamide, N,N dimethylacetamide, gamma butyrolacetone, ethylene carbonate, maleic acid, alpha-cyanoacetamide, and tris(dimethylamido) phosphate may be used.

In the treatment of the more soluble types of acrylonitrile polymers, for example those of from per cent to 75 per cent acrylonitrile and from per cent to 80 per cent of other monomers copolymerizable therewith, the selection of a solvent is less critical. This type of copolymer may be dissolved or otherwise physically affected by the various ketones, esters and aromatic hydrocarbon types of solvents. In general, the copolymer is placed in a suitable solution, or softened and swelled by the selected medium so as to enable a more ready dispersion of the aluminum salt within the solid polymer. Obviously a solvent which is also capable of dissolving at least to some extent the aluminum salt to be used will be exceptionally beneficial. However, the selection of the dispersing agent, the stabilizing agent and the particular method of dispersing the salt in the solid polymer is a matter readily determined by one skilled in the art.

To evaluate the stabilizing action of various compounds, acrylonitrile polymers of different chemical and physical properties were used and the aluminum salts dispersed therein by a variety of methods.

Example Polyacrylonitrile was stabilized by dissolving it in N,N-dimethylformamide and adding to separate solutions two per cent of each of the various aluminum salts in the table below. Films were prepared therefrom and tested to determine the light transmission properties by photoelectric methods. the table below were measured after forty minutes and three hour periods of exposure at a temperature of 180 C. The ratings are expressed The transmission values set forth in 4 in the percentage of the transmission in excess of the transmission through a sample of the identical polymer not containing the stabilizing agent using a 410 millimicron filter in the photometer.

Aluminum borate +223 +3.7 Aluminum chloride +413 +5.9 Aluminum chloride 6H2O +38.2 +3.7 Aluminum sulfate 18H2O +465 +30.6 Aluminum nitrate 91-120 +36.4 +56.7

What we claim is:

1. The stable polymer of claim 9 wherein the aluminum salt is aluminum chloride.

2. The stable polymer of claim 9 wherein the aluminum salt is aluminum sulfate.

3. The stable polymer of claim 9 wherein the aluminum salt is aluminum nitrate.

4. The stable polymer of claim 9 wherein the aluminum salt is aluminum borate.

5. The stable polymer of claim 10 wherein the aluminum salt is aluminum chloride.

6. The stable polymer of claim 10 wherein the aluminum salt is aluminum sulfate.

7. The stable polymer of claim 10 wherein the aluminum salt is aluminum nitrate.

8. The stable polymer of claim 10 wherein the aluminum salt is aluminum borate.

9. A heat stable acrylonitrile polymer comprising a polymer of 20 to 100 per cent by weight of acrylonitrile and up to per cent of another olefinic monomer copolymerizable therewith, said polymer containing intimately dispersed therein from 0.01 to ten per cent by weight of an inorganic acid salt of aluminum selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum nitrate and aluminum borate.

10. A heat stable acrylonitrile polymer comprising a polymer of 20 to per cent by weight of acrylonitrile and up to 80 per cent of another olefinic monomer copolymerizable therewith, said polymer containing intimately dispersed therein from 0.1 to three per cent by weight of an inorganic acid salt of aluminum selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum nitrate and aluminum borate.

ROBERT J. SLOCOMBE. GEORGE L. WESP.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,140,921 Rein Dec. 20, 1938 2,356,767 Kropa Aug. 29, 1944 2,419,512 Vesce Apr. 22, 1947 2,507,142 Chaban May 9, 1950 2,562,191 Howerton July 31, 1951 

9. A HEAT STABLE ACRYLONITRILE POLYIMER COMPRISING A POLYMER OF 20 TO 100 PER CENT BY WEIGHT OF ACRYLONITRILE AND UP TO 80 PER CENT OF ANOTHER OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, SAID POLYMER CONTAINING INTIMATELY DISPERSED THEREIN FROM 0.01 TO TEN PER CENT BY WEIGHT OF AN INORGANIC ACID SALT OF ALUMINUM SELECTED FROM GROUP CONSISTING OF ALUMINUM CHLORIDE, ALUMINUM SULFATE, ALUMINUM NITRATE AND ALUMINUM BORATE. 